The present invention relates to a coating method and apparatus, and, in particular, to a method and apparatus for coating a target object, such as a semiconductor wafer or an LCD substrate, with a processing liquid, such as a photo-resist liquid, which undesirably tends to become dry. The semiconductor process includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having, for example, wiring layers and electrodes to be connected to a semiconductor device on a target object, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target object.
In a process of manufacturing a semiconductor device or an LCD, coating apparatuses are utilized in various steps. A representative one of them is a coating apparatus of a photo-resist liquid, employed in a coating and developing system of the photo-resist. The photo-resist liquid is applied onto a target layer to be pattern-etched, such as a semiconductor, insulating, or conductive layer on a semiconductor, to form a photo-resist film on the target layer. The photo-resist film is exposed to light through a predetermined mask and is developed so that the film is patterned to copy the mask. Then, the target layer is etched, using the patterned photo-resist film as a mask.
A coating method as shown in FIG. 6A is known as a coating method of a photo-resist liquid. This method employs a nozzle 3 for supplying a processing liquid 4, i.e., a photo-resist liquid formed by dissolving a photo-sensitive resin in a solvent, and a spin chuck 1 for holding a semiconductor wafer W. During a coating process, the processing liquid 4 is supplied, i.e., dropped onto the wafer W from the nozzle 3 arranged above the spin chuck 1, while the spin chuck 1 is rotated. As a result, the processing liquid 4 is diffused from the central portion of the wafer W to its peripheral portion, so that the entire top surface of the wafer is uniformly coated with a photo-resist film.
In such a coating apparatus, if the processing liquid, i.e., the photo-resist liquid 4, hardens in the nozzle 3, problems arise such that the nozzle 3 becomes plugged and hardly any uniform photo-resist film is formed. The processing liquid 4 hardens mainly due to the processing liquid 4 becoming dry while the nozzle 3 is in a waiting state. In order to solve this problem, a method of preventing the photo-resist liquid from drying at a wait position of the nozzle 3 has been developed, as shown in FIG. 6B. This method employs a roller 5 having a lower part dipped in thinner 6 which is a solvent for the processing liquid, i.e., the photo-resist liquid 4. The processing liquid 4 is delivered from the nozzle 3 onto the roller 5 while the processing liquid 4 is removed from the roller 5 by a fixed wiper 7.
Since the tip port of the nozzle 3 is provided with the thinner 6 drawn up by the roller 5 in this method, the tip port of the nozzle 3 is prevented from drying. However, the processing liquid is constantly delivered in the waiting state, resulting in a waste of the processing liquid. If the processing liquid temporarily stops being delivered, the thinner 6 on the roller 5 is removed by the wiper 7, thereby bringing about problems such that the tip port of the nozzle 3 dries and the processing liquid deteriorates or hardens.
The wiper 7 plays an important role in removing the processing liquid and the like adhered to the roller 5, and, therefore, should not be omitted. Without the wiper 7, the processing liquid would deteriorate by transfer of substances from the roller 5 onto the tip port of the nozzle, resulting in hardly any coating film of a uniform thickness being obtained.